1. Field of the Invention
The present invention relates to a digital filter having phase-adjustment ability, and more particularly to a digital filter system which can restore the phase of data transmitted via digital radio communication and thereby enhances the noise-immunity of data and the correct bit decision.
2. Description of the Prior Art
Living in this modern society featured with highly developed information science, people face the necessity of exchanging information with others everyday. The way of transmitting information becomes more and more important. It has become very popular for people to use digital radio signals in their remote and non-face-to-face communication.
High-frequency signals received by a receiver of a digital radio communication equipment are demodulated. The resulting digital signals are usually distorted by external noises combined with the signals. Therefore, a digital filter is required to filter out such noises so that a modified and correct wave form of the received digital signals can be obtained to allow completely correct decision of data based on the received signals. Most conventional digital wave filters are so designed that their sampling frequency and count sampling point will cause the following drawbacks:
1. Data obtained from the filtered signals shall have inconsistant lengths, that is, the wave forms of high level 1 and low level 0 are uneven. Therefore, it is possible that an incorrect signal is read during data decision.
2. In addition, since it is not easy to decide whether a wave form is really delayed, temporarily delayed, or simply incorrectly read due to too many noises, it is usually to process the phase adjustment after wave filtering with complicated logical procedures through multi-level state control, such as an IF-THEN statement. However, in view of the responding speed of such phase adjustment, it is possible to have a response that is too slow.
It is therefore the inventor has developed a means to eliminate the above-mentioned drawbacks existed in the conventional digital filter systems.